IDENTIFICATION AND CHARACTERIZATION OF CULTIVAR-SPECIFIC 22-KDA HEAT-SHOCK PROTEINS FROM MITOCHONDRIA OF PISUM-SATIVUM

Pea plants (Pisum sativum L. cv. Feltham First) exposed to a heat stre ss of 37 degrees C for 6 h accumulated two low molecular weight (LMW) heat shock proteins (HSPs) of molecular mass 22 kDa. The two LMW HSPs were associated with purified mitochondria. N-terminal amino acid sequ encing analysis indicates that the more basic of these proteins is a n ovel protein. The response of other cultivars of P. sativum to heat sh ock revealed that up to three 22-kDa HSPs were expressed in a cultivar -specific manner. Evidence presented suggests that the different 22-kD a HSPs arise as a result of there bring multiple 22-kDa HSP genes. The expression of the most basic novel HSP was studied in the Feltham Fir st cultivar using two dimensional SDS-PAGE. Treatment of intact plants with chloramphenicol and cycloheximide prior to heat stress treatment indicated that the LMW HSPs were nuclear encoded and de novo synthesi sed. The response to heat shock was rapid with protein expression dete cted within 45 min and the protein remained in excess of 6 days follow ing removal of the stress. The protein accumulated to very high levels with maximal expression being 2% of the total mitochondrial protein. The results are discussed in relation to the likely role of LMW HSPs i n thermotolerance.